tidu873a | ti.com - semiconductor company | ti.com

R LIMIT

Low-voltage DC/DC (Fly-BuckTM) LM5160

To MCU

LDO

LDO

R ISOR CAL

Main BoardDaughter Board

R ISO = Insulation resistanceR CAL = Calibration resistance

10-V to 20-V DC

Basic isolation

V SENSE

V SENSE

500-V DC

5V_VCC1

5V_VCC2

MUXTS5A23157

CSMINA225

Digital ISOIsolator 7640

Flyback(DC/DC)

UCC28711

150-V to 800-V DC

AM

C1200

TI DesignsLeakage Current Measurement Reference Design forDetermining Insulation Resistance

Design Overview Design FeaturesThis TI design provides a reference solution to • Leakage Current Measurement Circuit With Optionmeasure the insulation resistance up to 100 MΩ. The for Programmable Current Sense Amplifier anddesign has an onboard, isolated 500-V DC power Switchable Shunt Resistorssupply and an isolated signal conditioning circuit to • Range of Measurement: 0 Ω to 100 MΩmeasure the leakage current and then determine the

• Measurement Accuracy: 5% (Uncalibrated)insulation resistance.• Test Voltage Level Derived from IEEE 43-2000

Design Resources • Onboard Isolated 500-V Power Supply to MeasureInsulation Resistance

Tool Folder Containing Design FilesTIDA-00440• Provision for Calibration Resistor on BoardINA225 Product Folder• Provision for Polarization Index MeasurementAMC1200 Product Folder

Based on Test DurationCSD13202Q2 Product Folder• Basic Isolation for Measurement CircuitISO7640FM Product Folder

INA333 Product Folder • Onboard Relay to Disconnect the InsulationTS5A23157 Product Folder Measurement Circuit When Not in OperationLM5160 Product Folder

Featured ApplicationsTLV1117-50 Product FolderLP2985A-50 Product Folder • Industrial DrivesUCC28711 Product Folder • Variable Speed AC/DC Drives

• Servo DrivesASK Our E2E Experts • TransformersWEBENCH® Calculator Tools • Solar Inverters

An IMPORTANT NOTICE at the end of this TI reference design addresses authorized use, intellectual property matters and otherimportant disclaimers and information.

1TIDU873A–April 2015–Revised April 2015 Leakage Current Measurement Reference Design for Determining InsulationResistanceSubmit Documentation Feedback

Copyright © 2015, Texas Instruments Incorporated

http://www.ti.com/tool/TIDA-00440

http://www.ti.com/product/INA225

http://www.ti.com/product/AMC1200

http://www.ti.com/product/CSD13202Q2

http://www.ti.com/product/ISO7640FM

http://www.ti.com/product/INA333

http://www.ti.com/product/TS5A23157

http://www.ti.com/product/LM5160

http://www.ti.com/product/TLV1117-50

http://www.ti.com/product/LP2985A-50

http://www.ti.com/product/UCC28711

http://e2e.ti.com/

http://e2e.ti.com/support/development_tools/webench_design_center/default.aspx

http://e2e.ti.com

http://www.go-dsp.com/forms/techdoc/doc_feedback.htm?litnum=TIDU873A

Introduction www.ti.com

1 IntroductionThe deterioration of insulation is one of the primary causes of electrical equipment failure. This TI designprovides a reference solution to measure the insulation resistance up to 100 MΩ with an uncalibratedaccuracy of 5%. The reference design uses an onboard isolated 500-V DC power supply and isolatedsignal conditioning circuit to measure the leakage current for determining the insulation resistance.

1.1 Importance of Insulation MeasurementInsulating materials play a critical role in the life of electrical equipment. The failure of insulation, while inservice, may cause significant damage to equipment and to the system to which the equipment isconnected. Insulation failure can cause dangerous voltage, fire, high fault current and explosion, damageto equipment and property, personnel injury, and fatal accident. By applying insulation tests, the user canidentify deteriorated insulation before any failure occurs.

1.2 Causes of Insulation DegradationThe main causes of insulation failure are dielectric contamination, temperature cycling, excessiveoverloads, excessive voltage stress due to overvoltage, and aging.1. Thermal stress: Running the machine in excessively hot or cold conditions causes over expansion or

contraction of the insulation, which may result in cracks and failures. However, thermal stresses arealso incurred every time a machine starts or stops. Unless the machinery is designed for intermittentuse, every stop and start adversely affects the aging process of the insulation.

2. Electric stress: Insulation is designed for a particular application. Overvoltages cause abnormal stresswithin the insulation, which can lead to cracking or delamination of the insulation.

3. Voltage unbalance: When the voltage between all three phases is equal (balanced), the current valuesare the same in each phase winding. When the voltages between the three phases (AB, BC, and CA)are not equal (unbalanced), the current increases dramatically in the motor windings. If the user allowsthis increase to continue for too long, the motor is damaged.

Normal cycles of operation lead to aging through the previously mentioned mechanisms. The aging ofinsulation is a slow process of degradation as these factors interact with each other in a gradual spiral ofdecline. At some point, depending on both original and operating conditions, the decline may speed upsignificantly.

2 Leakage Current Measurement Reference Design for Determining Insulation TIDU873A–April 2015–Revised April 2015Resistance Submit Documentation Feedback


http://www.ti.com


www.ti.com System Description

2 System DescriptionThe TIDA-00440 reference design uses a mechanism to find the leakage current and detect the failure ininsulation. The leakage current is measured by applying a fixed, high voltage DC and by measuring theleakage current flowing through the shunt. The high voltage DC is generated using an onboard powersupply based on a flyback topology, which takes a wide range of DC input voltage from 150-V DC to800-V DC. The functionality of finding insulation resistance is implemented using two boards: the mainboard (TIDA-00440MB), which is the signal conditioning circuit , and the daughter board (TIDA-00440DB),which has an Isolated 500-V DC.

One important point to note is that the test levels, test voltage, and insulation levels derive from the IEEEstandard IEEE43-2000 (IEEE Recommended Practice for Testing Insulation Resistance of RotatingMachinery [1]). This standard describes a recommended procedure for measuring insulation resistanceand describes the typical insulation resistance characteristics of rotating machine windings and how thesecharacteristics indicate winding condition. This standard recommends the minimum acceptable values ofinsulation resistance for AC and DC rotating machine windings. Using this standard as a base, Table 1makes the following judgments:

Table 1. Insulation Resistance

INSULATION JUDGEMENTRESISTANCE100 MΩ or higher Acceptable.

10 to 100 MΩ The winding has begun deteriorating. There is no problem with the performanceat present. Be sure to perform a periodic inspection.

1 to 10 MΩ The winding has considerably deteriorated. Special care is required. Be sure toperform a periodic inspection.

Lower than 1 MΩ Unacceptable.

3 Design FeaturesThe TIDA-00440 reference design features the following characteristics:1. Leakage current measurement circuit with option for:

(a) Programmable current sense amplifier: INA225 has four gain-settings selected based on the GS0and GS1

(b) Switchable shunt resistors2. Facilitates online insulation measurement during installation and maintenance testing3. Range of measurement: 0 Ω to 100 MΩ4. Measurement accuracy: 5% (Uncalibrated)5. Test voltage Level derived from IEEE 43-2000 (Recommended Practice for Testing Insulation

Resistance of Rotating Machinery)6. Onboard isolated 500-V power supply to measure insulation resistance7. Provision for calibration resistor on board8. Provision for polarization index measurement based on test duration9. Basic isolation for measurement circuit10. Onboard relay to disconnect the insulation measurement circuit when not in operation



http://www.ti.com


R LIMIT

Low-voltage DC/DC (Fly-BuckTM) LM5160

To MCU

LDO

LDO

R ISOR CAL

Main BoardDaughter Board

R ISO = Insulation resistanceR CAL = Calibration resistance

10-V to 20-V DC

Basic isolation

V SENSE

V SENSE

500-V DC

5V_VCC1

5V_VCC2

MUXTS5A23157

CSMINA225

Digital ISOIsolator 7640

Flyback(DC/DC)

UCC28711

150-V to 800-V DC

AM

C1200

Block Diagram www.ti.com

4 Block Diagram

Figure 1. High-Level Block Diagram of Measurement Circuit

Figure 1 shows the high-level block diagram of the measurement circuit. As previously mentioned, thisdesign consists of two boards: one main board (TIDA-00440MB) and one daughter board(TIDA-00440DB). The flyback (DC/DC) block on the left side of Figure 1 is the daughter board. All theremaining blocks are present on the main board.

The leakage current is measured by applying a fixed voltage and measuring the voltage across the shuntthat is a result of the leakage current. The reference design uses different switchable shunt resistances,which are switched on in a sequence to measure the insulation resistance. When there is a dead short,the insulation resistance is 0 Ω and a full current (or maximum) can pass through the insulation resistance.At this point in the measurement having a smaller shunt value (by turning on all of the switches) ismandatory. In the other case, when the insulation is higher, a higher shunt value is required. The leakagecurrent flowing through the shunt or shunts is measured using a current shunt monitor (INA225). Theleakage current is amplified with different gains (if required), which can be programmed using pins GS0and GS1 of the INA225 device. If using the gain of the INA225 is not required, the voltage across theshunt can be routed directly by using an onboard multiplexer (TS5A23157). The measured output voltageis isolated using an isolated amplifier (AMC1200), which has an output that can connect to an MCU. Theswitchable shunts and the multiplexer (MUX) channels are controlled through DIP switches, which areisolated using a digital isolator (ISO7640FM). The DIP switches are used to emulate the signals comingfrom the MCU to change the gain and shunts. The board operates from 15 V and then generates twoisolated 5-V rails through the Fly-Buck. The primary side generates 3.3 V.

The daughter board consists of an isolated discontinuous mode (DCM) flyback circuit for generating500-V DC from an input voltage ranging from 150-V DC to 800-V DC. On the main board, there is aprovision to measure the 500-V DC output voltage for diagnostic purposes.



http://www.ti.com


www.ti.com Block Diagram

4.1 Highlighted ProductsThe TIDA-00440 reference design features the following devices, which were selected based on theirspecifications.1. INA225 — Programmable gain, voltage output, and current shunt monitor2. AMC1200 — Precision fully-differential isolation amplifier3. LM5160 — Wide input, 1.5-A synchrounous Fly-Buck converter4. UCC28711 — Constant-voltage, constant-current controller with primary-side regulation5. CSD13202Q2 — 12-V, N-channel NexFET™ power MOSFETs6. ISO7640FM — Low-power, quad-channel digital isolators7. TS5A23157 — Dual 10-Ω SPDT analog switch8. TLV1117-50 — 800-mA, 5-V fixed, low drop-out voltage regulator9. LP2985A-50 — 150-mA, 5-V fixed, low drop-out voltage regulator10. INA333 — Low power instrumentation amplifier

For more information on each of these devices, see the respective product folders at www.ti.com or clickon the links for the product folders on the first page of this reference design guide.



http://www.ti.com

https://www.ti.com/


S8S

4

G3

1256D

7

Q1

TR-CSD13202Q2

500V+

500V-

SW1 S8S

4

G3

1256D

7

Q2

TR-CSD13202Q2

SW2

ISENSE

2.00k

R14

2.00k

R15

10.0k

R16

10.0k

R17

1 2

JD3

5-534206-1

12

JD4

5-534206-1

MID

0

R45

GND2

0

R8

499k

R2

499k

R59

499k

R62

499k

R61

220k

R13

2.70k

R12

261

R11

IN11

NO12

GND3

NO24

IN25

COM26

NC27

V+8

NC19

COM110

U10

TS5A23157DGS

IN+1

GND2

VS3

OUT4

GS05

GS16

REF7

IN-8

U3

INA225AIDGK

1

2

3

4

5

6

7

8

+

-

V+

V-

V-

V+

U4

AMC1200BDWV

1µFC4

470R21

470R23

GND

5V_VCC1

3V3

ISENSE

5V_VCC1

0R30

0R33

5V_VCC1

0R31

0R34

5V_VCC1

MUX

MUX

5V_VCC1

ISENSE

MID

GND1GND1

GND1

GND1

GND1

CSM(+)

CSM(-)

0

R32 SW2

1µFC6

1000pF

C512

J8

282834-2

0R55

GND1

MID

5V

D10

SM

BJ5

.0A

-13-F

0.01µFC43

0.01µFC42

GND1

GND1

0.1µFC39

GND1

0.1µFC38

GND1

0.1µFC40

GND

0.1µFC41

GND1

10.0

R25

10.0

R18

10.0

R20

10.0

R24

GS0 GS1 GAIN==================GND GND 25V/VGND VS 50V/VVS GND 100V/VVS VS 200V/V

Principle of Operation www.ti.com

5 Principle of Operation

5.1 Current-Shunt ApproachThis design uses a current-shunt approach to measure the insulation resistance. Figure 2 shows aschematic of the current-shunt approach. The circuit consists of three stages: the current shunt monitor,multiplexer, and isolation amplifier.

Figure 2. Signal Chain for Current Shunt Method

Multiple shunts are used in this design, which is important to note. Figure 3 shows the shunt resistorsused for the insulation measurement. R13 is the fixed shunt and R11−R12 are switched on and off byusing two MOSFETs (Q1 and Q2), respectively. Both of the MOSFETs are CSD13202Q2 logic-levelNexFETs from TI.

Figure 3. Schematic With Multiple Shunts



http://www.ti.com


IN11

NO12

GND3

NO24

IN25

COM26

NC27

V+8

NC19

COM110

U10

TS5A23157DGS

IN+1

GND2

VS3

OUT4

GS05

GS16

REF7

IN-8

U3

INA225AIDGK

1µFC4

ISENSE

5V_VCC1

0R30

0R33

5V_VCC1

0R31

0R34

5V_VCC1

MUX

MUX

5V_VCC1

ISENSE

MID

GND1GND1

GND1

GND1

0

R32 SW2

1µFC6

0R55

GND1

MID

5V

D10

SM

BJ5

.0A

-13

-F

0.01µFC43

0.01µFC42

GND1

GND1

0.1µFC39

GND1

0.1µFC41

GND1

10.0

R25

10.0

R18

10.0

R20

10.0

R24

GS0 GS1 GAIN==================GND GND 25V/VGND VS 50V/VVS GND 100V/VVS VS 200V/V

www.ti.com Principle of Operation

The current shunt monitor used in this design is INA225 (see Figure 4). The voltage across the shunt(between the ISENSE and MID points in the schematic) is connected to the inputs of INA225. The boardhas provisions to ensure protection, such as a 5-V clamp diode (D10) and differential caps (C42 and C43).These protections are currently not populated on the board and are marked as do not populate (DNP).The gain of INA225 is programmable and can be set by using the GS0 and GS1 pins. Table 2 shows thegain setting for INA225. The gain can also be programmed using a signal SW2 coming from the digitalisolator.

Table 2. Gain Setting for INA225

GAIN GS0 GS125 V/V GND GND50 V/V GND VS

100 V/V VS GND200 V/V VS VS

The TS5A23157 is an analog multiplexer with two differential channels. One channel is connected to theoutput of INA225 and the second channel is connected directly to the sense signal (between ISENSE andMID). The selection between the two differential channels of TS5A23157 is controlled by the signal MUX,coming from the digital isolator. During scenarios of high leakage current, gain may not be required andthe INA225 monitor can be bypassed using the TS5A23157 device.

NOTE: When INA225 is not used for providing the gain, TI recommends to unpopulate R20 and R24to prevent any effect due to the input impedance of INA225.

Figure 4. INA225 and TS5A23157 Section for Current Shunt Method



http://www.ti.com


499 k

R11 R12

RINSULATION

INA225 TS5A23157 J8R13

R45

R8 = 0

Q1 Q2

+

t

500-V DC

coming

from

daughter

board

AM

C1200

GS0 GS1 MUX

(Q1 and Q2 are open)

MID

ISENSE

IN11

NO12

GND3

NO24

IN25

COM26

NC27

V+8

NC19

COM110

U10

TS5A23157DGS

1

2

3

4

5

6

7

8

+

-

V+

V-

V-

V+

U4

AMC1200BDWV

1µFC4

470R21

470R23

GND

5V_VCC1

3V3

MUX

MUX

5V_VCC1

ISENSE

MID

GND1

GND1

CSM(+)

CSM(-)1000pF

C512

J8

282834-2

0.1µFC38

GND1

0.1µFC40

GND

0.1µFC41

GND1

10.0

R25

10.0

R18


The output of TS5A23157 is connected to the isolated amplifier AMC1200 (see Figure 5). The non-isolated side of AMC1200 is powered with 5V_VCC1 coming from the TLV1117-50. The isolated side ofAMC1200 is powered with 3.3 V coming from the LM5160 Fly-Buck power supply section. Both of thesupplies are decoupled using 0.1-μF capacitors (C38 and C40 respectively). The differential output ofAMC1200 is available on terminal J8.

Figure 5. AMC1200 Section of Current Shunt Method

5.1.1 Single-Shunt ApproachIn this approach, both the MOSFETs Q1 and Q2 are turned off using signals SW1 and SW2, respectively.So, the shunt resistor used in this case is R13 only (fixed at a value of 22 Ω). To cover the entire range ofinsulation resistance, the gain of INA225 is varied using GS0 and GS1 pins. Figure 6 shows the simplifiedconnection diagram for this approach. Section 8.2 shows the measurement accuracy for this approach.

Figure 6. Simplified Connection Diagram for Single-Shunt Approach



http://www.ti.com


RG1

VIN-2

VIN+3

V-4

REF5

OUT6

V+7

RG8

U1

INA333AIDGK

1

2

3

4

5

6

7

8

+

-

V+

V-

V-

V+

U2

AMC1200BDWV

100pFC2 1µF

C1470R5

470R7

GND

3V3

500V+

500V-6.8k

R6

ISENSEGND2

GND2

51kR10

Gain = 1 + (100k/RG)

RDM(+)

RDM(-)

1000pFC3 1

2

J7

282834-2

1 2

JD3

5-534206-1

12

JD4

5-534206-1

GND2

0R45

GND2

0

R8

5V_VCC25V_VCC2

5V

D9

SM

BJ

5.0

A-1

3-F

499k

R2

0.01µFC35

0.01µF

C15

GND2

GND2

0.1µFC12

GND2

0.1µFC13

0.1µFC14

GND2GND

For Resistive Divider based measurement:R13 = 0 ohm, R43 = DNP

10.0

R4

10.0

R9

7.50MR3

7.50M

R582 1

7.50M

R44

7.50MR60

7.50MR63

7.50M

R43

499k

R59

499k

R62

499k

R61

220kR13

2.70kR12

261R11

499 k

R11 R12

RINSULATION

TS5A23157 J8R13

R45

R8 = 0

Q1 Q2

+

t

500-V DC

coming

from

daughter

board

AM

C1200

MUX

(Q1 and Q2 are open and closed based on the requirement)

MID

ISENSE


5.1.2 Multiple-Shunt ApproachIn this approach, MOSFETs Q1 and Q2 are turned on or off based on the output voltage measured onterminal J8. The total shunt resistance can be a combination of R11, R12, and R13. In this approach,INA225 is not used (so R20 and R24 must be unpopulated). Figure 7 shows the simplified connectiondiagram for this approach. Section 8.1 shows the measurement accuracy for this approach.

Figure 7. Simplified Connection Diagram for Multiple-Shunt Approach

5.2 Resistive Divider ApproachThis design also uses the resistive divider approach to measure the insulation resistance. Figure 8 showsa schematic of the resistive divider approach.

Figure 8. Signal Chain for Resistive Divider Method



http://www.ti.com


1

2

3

4

5

6

7

8

+

-

V+

V-

V-

V+

U2

AMC1200BDWV

1µFC1

470R5

470R7

GND

3V3

GND2

RDM(+)

RDM(-)

1000pFC3 1

2

J7

282834-2

5V_VCC2

0.1µFC13

0.1µFC14

GND2GND10.0

R4

10.0

R9

RG1

VIN-2

VIN+3

V-4

REF5

OUT6

V+7

RG8

U1

INA333AIDGK

100pFC2

6.8k

R6

GND2

51kR10

Gain = 1 + (100k/RG)

GND2

5V_VCC2

5V

D9

SM

BJ5.0

A-1

3-F

0.01µFC35

0.01µF

C15

GND2

GND2

0.1µFC12

GND2

For Resistive Divider based measurement:R13 = 0 ohm, R43 = DNP

10.0

R4

10.0

R9

7.50MR3

7.50M

R582 1

7.50M

R44

7.50MR60

7.50MR63

7.50M

R43


The circuit consists of two stages: the instrumentation amplifier and an isolation amplifier. This referencedesign uses the instrumentation amplifier INA333 (see Figure 9).

Figure 9. INA333 Section for Resistive Divider Method

The 500-V DC coming from the daughter board is applied across the insulation resistance. The voltagedeveloped across the insulation resistance is divided by four resistors: R44, R58, R3, and R6. Animportant thing to note is that the total resistance is divided into three 7.5-MΩ resistors to reduce thevoltage stress on each of the resistors. A single high-voltage resistor is costly in comparison to the threedifferent low-voltage resistors. The voltage across R6 is fed to the input of the instrumentation amplifierINA333. One 100-pF capacitor (C2) is used as a filter for any noise present on the input signal. The boardhas provisions to ensure protection, such as a 5-V clamp diode (D9) and differential caps (C15 and C35).These protections are currently not populated on the board and are marked as DNP. The gain of theINA333 amplifier can be set by the RG pin (that is R10 in Figure 9) using the following formula:Gain = 1 + (100 k / RG) (1)

Currently the gain is set at unity because of the signal levels. The output of INA333 is connected to theisolated amplifier AMC1200 (see Figure 10).

NOTE: The primary reason for using an INA333 amplifier is to provide a high input impedance forthe measurement circuit. For lower-cost applications, a simple op-amp based, non-invertingunity-gain buffer can be used.

Figure 10. AMC1200 Section of Resistive Divider Method

The non-isolated side of the AMC1200 device is powered with 5V_VCC2 coming from the LP2985A-50.The isolated side of the AMC1200 device is powered with 3.3 V coming from the LM5160 Fly-Bucksection. Both of the supplies are decoupled using 0.1-μF capacitors (C13 and C14, respectively). Thedifferential output of the AMC1200 is available on terminal J7.



http://www.ti.com


+

RGV+

Ref

Out

V-

-

RG

2

1

8

3

7

5

6

4

GND2

GND2

V6 5

V5 0

+

-

U6 INA 333

TERMINAL 2

GND2

TERMINAL 1

AM1

VM1

+

+

VS1 250

VS2 250

R1 499k

R4 0

VDC_PLUS

VDC_MINUS

Riso 10M

R12 22.5M

R2 6.8k C5 100p

GND2

+

-

VIN P

VDD1 VDD2

VOUT P

VOUT N

GND2GND1

VIN N

Vdd1 Vdd2

GND2GND2

VM4C3 1u

R11 10

R3 10

GND2

Vdd1 Vdd2

V4 5V3 5

+ +

+

+

+

-VM6C4 1n

R5 470

R6 470

U2 AMC1200

499 k

R11 R12

RINSULATION

INA333 J7R130

R8 = 0

Q1 Q2

+

t

500-V DC

coming

from

daughter

board

AM

C1200

(R13 = 0 )

6.8 k

R450

OR

Any non-investing unity gain buffers

22.5 M


Figure 11 shows a simplified circuit for the resistive divider approach.

Figure 11. Simplified Resistive Divider Approach

Figure 12 shows the TINA-TI™ simulation software for the resistive divider approach. The graph from theTINA-TI simulation (Figure 13) shows that, due to the ratio of resistors, the voltage across R6 does notvary linearly with the insulation resistance. The measured value of voltage at the output of AMC1200 isalmost saturated with an insulation resistance value greater than 15 MΩ. Section 8.3 shows the sameobservation during the testing and in the results.

Figure 12. TINA-TI Simulation for Resistive Divider Approach



http://www.ti.com



Figure 13. TINA-TI Graphs Showing Saturation

Though the resistive divider approach is investigated in this design, it is not useful as an approach tocover the entire range for insulation resistance up to 100 MΩ.



http://www.ti.com


1

2

3

4

5

6

7

8

+

-

V+

V-

V-

V+

U5

AMC1200BDWV

1µFC7

470R26

470R28

GND

3V3

5V_VCC2

500V+

500V-

HV_DC(+)

HV_DC(-)

Daughter Card (500Vdc)

GND2

500V_SENSE(+)

500V_SENSE(-)

3.0kR27

J1

J2

1000pFC8

12

J6

282834-2

1 2

JD1

5-534206-1

1 2

JD3

5-534206-1

12

JD4

5-534206-112

JD2

5-534206-1

GND2

0R56

GND2

0

R8

5V

D5

SM

BJ5.0

A-1

3-F

499k

R2

0.1µFC36

0.1µFC37

GND2GND10.0

R22

10.0

R29

0R57

3.0MR19

3.0MR65

3.0MR64

499k

R59

499k

R62

499k

R61

www.ti.com Circuit Design

6 Circuit Design

6.1 Sensing of 500-V DC for Resistive Divider ApproachTo measure the 500-V DC voltage, the design is provided with an isolated amplifier AMC1200. Figure 14shows a schematic of the AMC1200.

Figure 14. Sensing of 500-V DC Voltage

The 500-V input coming from the daughter card is stepped down using four resistors: R64, R65, R19, andR27. The voltage across R27 is taken as an input to the AMC1200. An important thing to note is that thetotal resistance is divided into three 3-MΩ resistors to reduce the voltage stress on each of the resistors.One single high-voltage resistor is costly in comparison to the three different low-voltage resistors. Theboard has a 5-V clamp diode (D5) if protection is required. This protection is currently not populated onthe board and is marked as DNP. The non-isolated side of the AMC1200 is powered with 5V_VCC2coming from the LP2985A-50. The isolated side of the AMC1200 is powered with 3.3 V coming from theLM5160 Fly-Buck section. Both the supplies are decoupled using 0.1-μF capacitors (C36 and C37,respectively). The differential output of the AMC1200 is available on terminal J6.

An important thing to note is that the input impedance of the AMC1200 amplifier is approximately 28 kΩ(typical). With such a high value for the sense resistor (R27 = 3 kΩ), the effect of input impedance mustbe considered. The current passing through each of the resistors must also be very low to reduce theoverall power consumption. In short, this trade-off must be addressed.



http://www.ti.com


100MegR35

5V_VCC1

D1

1S

S31

5T

PH

3F

J3

J4

1

8

2

7

5

34

6

K1

G2RL-2 DC5

RELAY

GND1

0

R36 1

32

,4

Q32DD1664R-13

GND2

0.1µFC44

GND1

MID

VCC11

GND12

INA3

INB4

INC5

IND6

NC7

GND18

GND29

EN10

OUTD11

OUTC12

OUTB13

OUTA14

GND215

VCC216

U11

ISO7640FM

GND

3V3

6 3

1827

5 4S1

78B04ST

3V3SW1

SW2

RELAY

MUX

5V_VCC1

0R41

0R42

5V_VCC1

GND1

GND1

GND1

0R37

0R38

0R39

0R40

0.1µFC10

0.1µFC9

GND

Circuit Design www.ti.com

6.2 Digital Isolator and DIP SwitchesAs previously mentioned, signals SW1 and SW2 control the MOSFETs in the current shunt method. TheMUX signal is used to select the input channel of the multiplexer TS5A23157. The signal RELAY controlsthe onboard relay. The intention of this design is to have all of these signals originate from an MCU in theend-application. To emulate this intention, the design uses four-channel DIP switches (see Figure 15).Because the MCU operates at 3.3 V and the control signals control the high-voltage circuits, isolating theMCU and high-voltage circuit is important. The ISO7640FM is a digital isolator from TI with four channels.The outputs are enabled when EN = 1. To enable and disable the outputs of the ISO7640FM, tworesistors are used (R41 and R42). R41 is currently populated, which means that the outputs are enabled.The isolated side of the ISO7640FM device is powered with 5V_VCC1 coming from the TLV1117-50; thenon-isolated side is powered with 3.3 V coming from the LM5160 Fly-Buck section. Both of the suppliesare decoupled using 0.1-μF capacitors (C9 and C10, respectively).

Figure 15. ISO7640FM With DIP Switches

6.3 Onboard RelayAs Figure 16 shows, the TIDA-00440 reference design uses one relay for connecting and disconnectingthe end equipment from the measurement circuit. The normally closed (NC) contacts of the relay areconnected to a calibration resistor R35. Banana terminals J3 and J4 are used for connecting the endequipment that requires insulation measurements. The relay is driven using a simple BJT, which iscontrolled by the signal RELAY originating from the digital isolator IS07640FM. Because the applicationrequires a high voltage of 500 V, selecting the relay with the proper creepage and clearances is important.

Figure 16. Relay for On-the-Fly Connection of Insulation Resistance to Measurement Circuit



http://www.ti.com


Fly-buck

LDO

LDO

5V_VCC1

5V_VCC23V3 Pri

(non-iso)

15 V Nominal(10 V to 20 V)


6.4 Calculation of Power Consumption for All ComponentsFigure 17 shows the scheme for the power supply. The operating input voltage range for the Fly-Buckpower supply is 10-V DC to 20-V DC. The 3.3 V (required to power the non-isolated side) generates fromthe primary winding of the Fly-Buck. Two +6-V outputs generated from the Fly-Buck transformer areconverted to +5-V outputs, each using two different LDOs. The +5V_VCC1 is used to power themeasurement circuit for the current-shunt approach and the relay. The +5V_VCC2 is used to power themeasurement circuit for the resistive divider approach.

Figure 17. Scheme for Power Supply Section

Table 3 shows the total power consumption calculation for the design.

Table 3. Calculation of Power for Each Onboard Device

TOTAL SELECTED LDOPOWER MAX CURRENT SUPPLY POWERSR. OUTPUT SHOULD HAVENAME OF THE IC SUPPLY TAKEN BY IC VOLTAGE CONSUMPTIONNO. CURRENT OUTPUTUSED (IN A) (IN V) (IN W) (IN A) CURRENT OF1 INA333 5V_VCC(2) 0.01 5 0.05

AMC12002 (resistive divider 5V_VCC(2) 0.065 5 0.325

approach) primary 0.14 0.15AMC1200 (500-V

3 DC sensing) 5V_VCC(2) 0.065 5 0.325primary

4 INA225 5V_VCC(1) 0.03 5 0.15AMC1200 (current

5 shunt approach) 5V_VCC(1) 0.065 5 0.325primary

0.23749 0.256 TS5A23157 5V_VCC(1) 0.02 5 0.1ISO7640FM7 5V_VCC(1) 0.04249 5 0.21245secondary

8 Relay 5V_VCC(1) 0.08 5 0.4AMC1200

(resistive divider 3V3_Pri (non-9 0.06 3.3 0.198approach) iso)secondary

AMC1200 (current 3V3_Pri (non-10 shunt approach) 0.06 3.3 0.198iso) 0.02103717 0.2secondaryAMC1200 (500-V 3V3_Pri (non-11 DC sensing) 0.06 3.3 0.198iso)secondary

ISO7640FM 3V3_Pri (non-12 0.0063749 3.3 0.02103717primary iso)



http://www.ti.com


126kR46

GND

0.1µFC29

22µFC32

22µFC33

GND GND

1µFC34

GND

10µFC28

1000pFC31

0.01µFC22

V(PRI)3V31

2J5

282834-2

1.00kR1

Green

12

D6

GND

AGND1

PGND2

VIN3

EN/UVLO4

RON5

SS6

FPWM7

FB8

VCC9

BST10

SW11

SW12

PAD13

U6

LM5160ADNTR

0.01µFC11

GND

GND

19.6kR51

145k

R49

35.2k

R48

0.01µF

C24

12.7kR50

20.0kR52

VIN+GND

Vin(nom) = 15V DCVin range = 10V to20V DC

2ms Soft Start

fsw = 250kHz

SW

D4

10BQ040TRPBF8

12

4

3

11

15

T1

750342773SW


For the calculation of individual devices, refer to the specific datasheet. Table 4 shows the selection ofLDOs, which is based on the output currents and the power levels required.

Table 4. Final Selection of LDOs

LDO SELECTIONPOWER SUPPLY INPUT OUTPUT OUTPUT PART NUMBER PACKAGENAME ON BOARD VOLTAGE VOLTAGE CURRENT

5V_VCC(1) 6 5 0.25 TLV1117-50 8 SON5V_VCC(2) 6 5 0.15 LP2985A-50 SOT-23

3V3 15 (20 V max) 3.3 3.3 – –

6.5 Design of Fly-Buck Power Supply Using LM5160The primary goal of this design is to provide a high-performance, cost-effective, and easy-to-designisolated power supply solution. The Fly-Buck is basically a buck regulator with couple windings added tothe inductor. The coupled windings can generate isolated outputs. View more details about this topology inAppendix A—Fly-Buck Power Supply.

6.5.1 Setting the Primary Side Output VoltageThe primary-side regulation (PSR) of the Fly-Buck topology is realized through the coupled winding of thetransformer, as the primary output clamps the secondary outputs during the duty-off time. Setting theprimary output is the first step in a Fly-Buck converter design. Having the duty cycle below 50% is optimalbecause the Fly-Buck secondary outputs transfer the energy in off-time; and having a duty cycle too highaffects the energy flow. Based on VPRI = D × VIN, the primary side output is initially set at 3.3 V, whichgives 33% of D at the minimum of VIN = 10 V. Then the secondary-to-primary turns ratio of the transformercan be estimated as N = VSEC / VPRI = 1.91, and the primary-side average current at full-load is roughlyiopri + 2(N × iosec) = 1.155 A, accounting for a 250-mA current on each of the secondary outputs. Theseparameters must be tuned and adjusted during the design process. In the final design, the primary outputvoltage is settled at 3.3 V, as Figure 18 shows.

Figure 18. Primary Section of Fly-Buck Using LM5160

6.5.2 Transformer DesignThe desirable transformer turns ratio is calculated based on the secondary-to-primary output ratio, whichis 1.91:1. The rectifier diode forward voltage and winding data capture record (DCR) drop must be takeninto account. The turns-ratio also has a certain granularity limit subject to the actual winding turn count. Toaccommodate that granularity limit, adjust the primary output voltage accordingly.

The primary side inductance determines the current ripple in the transformer. The LM5160 device limitsthe peak current to approximately 2.1 A, and from the estimated 1.155-A average current level, there isplenty of ripple margin.



http://www.ti.com


D3

10BQ040TRPBF

D2

10BQ040TRPBF

1µF

C16

1µF

C23

GND2

10µFC17

10µFC21

6V_VCC1

6V_VCC28

12

4

3

11

15

T1

750342773

4

3

11

12

15

8

PRISEC6 V

0.4 A

SEC6 V

0.4 A


The transformer used in this design is built with an EPW15-core through-hole package by WurthElektronik and the part number is 750342773. The transformer specification has a secondary-to-primaryturns ratio of 1.91:1, and both the secondary windings have the same turn count. The primary inductanceis 60 μH. Figure 19 shows the symbol for this transformer. The following list shows the isolation levels:1. Between primary and secondary: Creepage (9.2 mm) and clearance (8 mm)2. Between primary and secondary: 1.5-kV AC, one-minute isolation (dielectric rating) between primary

and secondary3. Isolation between primary and secondary pass: 7.4 kV impulse test voltage (1.2/50 µsec)4. Isolation between two secondaries: Clearance (5.5 mm) and type test = 1.8 kVRMS

Figure 19. Fly-Buck Transformer Symbol

6.5.3 Shutdown FunctionThe LM5160 has an undervoltage lock out (UVLO) pin for the low voltage shutdown, which can be utilizedas an enable function pin. External circuitry can be used to pull the UVLO pin to ground to shut down theoperation of the power supply.

6.5.4 Generating the Output VoltagesThe total output voltage from the secondary winding is 6 V on each winding. Figure 20 shows thesecondary section of the schematic.

Figure 20. Secondary Section of Fly-Buck Using LM5160



http://www.ti.com


D3

10BQ040TRPBF0R47

1µF

C23

IN1

OUT5

2

CBYP4

ON/OFF3

GND

U8

LP2985AIM5-5.0

1µFC27

GND2

GND2

10µFC21

1.00kR54

Green

12

D8

GND2

0.1µFC25

0.1µFC26

1000pFC30

5V_VCC25V_VCC2

6V_VCC28

12

4

3

11

15

T1

750342773

D2

10BQ040TRPBF

1µFC20

1µF

C16

1

VIN2

VIN3

VIN4

VOUT5

VOUT6

VOUT7

NC8

VOUT9

GND

U7

TLV1117-50IDRJR

GND1

10µFC17

1.00kR53

Green

12

D7

GND1

0.1µFC19

0.1µFC18

5V_VCC15V_VCC1

6V_VCC1

8

12

4

3

11

15

T1

750342773


6.6 Generating 5V_VCC1 and 5V_VCC2Each of the rails from the two isolated, 6-V rails (generated from the LM5160 Fly-Buck section) areconverted to 5 V by using two fixed output linear regulators TLV1117-50 and LP2985A-50.

The TLV1117-50 is a fixed, 5-V output, LDO regulator designed to provide up to 800 mA of output current.A 0.1-uF cap and a 1-uF cap are connected on both the input as well as the output sides of the LDO. Thelight-emitting diode (LED) D7 indicates when the +5V_VCC1 is available. Figure 21 shows the schematiccapture for the TLV1117-50 section.

Figure 21. TLV1117-50 for 5V_VCC1

LP2985A-50 is a fixed 5-V output, LDO regulator designed to provide up to 150 mA of output current. A0.1-uF cap and a 1-uF cap are connected on both the input as well as the output sides of the LDO. TheD8 LED indicates when the +5V_VCC2 is available. Figure 22 shows the schematic capture for theLP2985A-50 section.

Figure 22. LP2985A-50 for 5V_VCC2



http://www.ti.com



6.7 Design of Flyback Power Supply Using UCC28711 (TIDA-00440DB Daughter Board)

6.7.1 Requirements of the Power SupplyThe requirements of the main isolated power supply to be used in insulation measurement are as follows:1. Input range: 150-V DC to 800-V DC2. Output voltage: 500-V DC3. Output current: 2 mA (max)4. < 1% output ripple voltage5. Isolation: Functional6. Regulation: < 5%7. Size: As compact as possible8. Controller must be able to shut down the power supply when a measurement is not made

6.7.2 Circuit DesignTo translate the Section 6.7.1 Requirements of Power Supply to the sub-system level, Section 6.7.2.1through Section 6.7.2.3 lists the requirements of the PWM controller, MOSFETs, and transformer.

6.7.2.1 PWM ControllerBecause a ±5% regulation is acceptable, a PSR controller is feasible for this task. The primary-sidefeedback eliminates the requirement of using optocoupler feedback circuits. A device with discontinuousconduction mode with valley switching can minimize switching losses. The UCC28711 is a suitablecontroller for this application. The UCC28711 device is a flyback power-supply controller, which providesaccurate voltage and constant current regulation with primary-side feedback. The modulation scheme is acombination of frequency and primary peak-current modulation to provide high conversion efficiencyacross the load range. The controller has a maximum switching frequency of 106 kHz and allows for ashut-down operation using the NTC pin.

6.7.2.2 Transformer DesignThe transformer design has the following specifications:1. Input: 100-V DC to 850-V DC2. Frequency: 70 kHz (min)3. Ambient temperature: 60°C (max)4. Output: Split into two secondaries – each of 250-V DC at 25 mA5. Max. operating duration: 30 min6. Topology: Flyback (DCM)7. Controller to be used: UCC287118. Preferred core size: EE16 (EE16 core is required due to winding accommodation)9. Insulation: Functional10. Auxiliary winding: 15 V at 30 mA



http://www.ti.com


PGND

VDD1

VS2

NTC3

GND4

CS5

DRV6

HV8

U1

UCC28711D

NTC

PGND

VFB

VDD

1µFC5600V

D101N4937-E3

PGND

10 µFC4

1000pFC6

Green

A2

C1

LD1

6.80kR6

D9

D-1N4002

PGND

100R7

600V

D8

1N4937-E3

43.0kR8

15.0kR13

1

2

5

6

7

8

PRI100-V DC to 580-V DC

70 kHz

SEC 1250-V DC

25 mA

SEC 2250-V DC

25 mA

3

4

AUX15-V DC30 mA


Figure 23 shows the symbol for this transformer. The transformer used in this design is built with aEE16-core through-hole package by Wurth Elektronik, and the part number is 750342792. Thetransformer specification has a secondary-to-primary turns ratio of 2.88:1, and both the secondarywindings have the same turn count. The secondary-to-auxiliary turns ratio is 15.76:1. The primaryinductance is 736 μH.

Figure 23. Fly-Buck Transformer Symbol

6.7.2.3 Power MOSFETThe power MOSFET must have a rated drain to source voltage VDS ≥ 1100 V to support an 800-V DCinput and the power MOSFET must also support a 0.25-A (minimum) drain current. This reference designuses the IXTA06N120P, which is a 1200-V device with a drain current of 0.6 A.

6.7.2.4 Primary-Side RegulationIn primary-side control, the output voltage is sensed on the auxiliary winding during the transfer oftransformer energy to the secondary. Appendix B—PSR Flyback Power Supply provides more details onthe component selection.

Figure 24 shows the schematic section of the primary feedback.

Figure 24. Primary Feedback



http://www.ti.com


V = 21 VVDD_ON

VVDD

V = 8 VVDD_OFF

0 V

DRV

3 Initial DRV Pulses After VDD(ON)

PGND

HV_STARTVDD

1

VS2

NTC3

GND4

CS5

DRV6

HV8

U1

UCC28711D

10

R10 1

34

Q1IXTA06N120P

10kR12

PGND

390

R14

0.75R15

5100pFC7


The output overvoltage function is determined by the voltage feedback on the VS pin. If the voltagesample on VS exceeds 115% of the nominal VOUT, the device stops switching and also stops the internalcurrent consumption of IFAULT. Stopping the internal current consumption of IFAULT discharges the VDDcapacitor to the UVLO turn-off threshold. After this discharge, the device returns to the start state and astart-up sequence ensues.

Protection is included in the event of component failures on the VS pin. If complete loss of feedbackinformation on the VS pin occurs, the controller stops switching and restarts.

6.7.2.5 Current SensingFor this reference design, a 0.75-Ω resistor is selected based on a nominal maximum current-sense signalof 0.75 V. Figure 25 shows the current sense circuit of the schematic.

Figure 25. Current Sense

6.7.2.6 Power-On and HV Start-UpFigure 26 shows the power-on sequence for the UCC28711 device. When the VDD pin of the UCC28711reaches the VVDD_ON threshold, the device generates three initial drive pulses for the MOSFET. These drivepulses turn on the PWM controller with the help of a high-voltage startup (HV) pin.

Figure 26. Power-On Sequence



http://www.ti.com


HV_STARTVDD

1

VS2

NTC3

GND4

CS5

DRV6

HV8

U1

UCC28711D

10

R10 1

34

Q1IXTA06N120P

10kR12

PGND

DC+

1000V

D1

1N4007

470kR1

470kR2

470kR3

470kR5

HV_START

D6P4KE550

PGND

0.22µFC1

PGND

1 2JD1

61300211121


The UCC28711 device has an internal 700-V startup switch. Because the DC bus can be as high as800-V DC, an external Zener voltage regulator is used to limit the voltage at the HV pin to about550-V DC. The typical startup current is approximately 300 μA, which provides fast charging of the VDDcapacitor. The internal HV startup device is active until VDD exceeds the turn-on UVLO threshold of 21 V,at which time the HV startup device is turned off. In the off state, the leakage current is very low tominimize standby losses of the controller. When the VDD falls below the 8.1-V UVLO turn-off threshold,the HV startup device is turned on. Figure 27 shows the HV startup circuit.

Figure 27. HV Startup

6.7.2.7 MOSFET Gate DriveThe DRV pin of the UCC28711 device is connected to the MOSFET gate pin through a series resistor.The gate driver provides a gate drive signal limited to 14 V. The turnon characteristic of the driver is a25-mA current source, which limits the turnon dv/dt of the MOSFET drain. This characteristic reduces theleading-edge current spike, but still provides a gate drive current to overcome the Miller plateau. The gate-drive turnoff current is determined by the low-side driver RDS_ON and any external gate-drive resistance.Figure 28 shows the gate drive for MOSFET.

Figure 28. MOSFET Gate Drive



http://www.ti.com


PGND

VFB

GND_ISO

3kV

D3

GP02-30-E3/73

D7P4KE5500

R160.47µFC9

1.02MR18

1.02MR19

0.47µFC3

3kV

D4

GP02-30-E3/73

1

3

2

4

5

6

7

8

T1

750342792

PRI

AUX

SEC1

SEC2

0.47µFC8

1

2

4

3

U2

ACPL-217-56AE

100

R9

GND

100k

R11

PGND PGND

NTC

1

2

J1

61300211121


6.7.2.8 Shutdown Mechanism for UCC28711The NTC pin of the UCC28711 device can be pulled down to shut down the PWM operation of the device.Figure 29 shows the isolated shutdown mechanism for the UCC28711 using an optocoupler. In situationsthat do not require measuring the insulation resistance, use a SHUTDOWN signal coming from anyavailable MCU in the application to shut off the 500-V DC output.

Figure 29. Isolated Shutdown for UCC28711

6.7.2.9 Generating Isolated 500-V DC OutputThe two secondary windings of the transformer produce 250 V each while regulating. To generate 500 V,use a simple voltage doubler, as Figure 30 shows. In the case of a no-load condition, or during anyabnormal condition, if the output tries to go much higher, a 550-V Zener (connected across the output)protects the output from going out of regulation.

Figure 30. Generation of 500-V Output Using Voltage Doubler



http://www.ti.com


T1 T2 T3

Connect to any one terminal

F

Connect to motor frame

TIDA-00440

Earth

Frame

xxHP30ACIM

T1 T2

Connect to any one terminal

TIDA-00440

Earth

Applications www.ti.com

7 ApplicationsInsulation measurement is important for a number of applications. Some of the applications includetransformers, solar inverters, industrial motor drives (variable speed AC/DC drives, servo drives), and soforth. Figure 31 and Figure 32 show two of these applications.

Figure 31. Measurement of Insulation Resistance for HV Transformer

Figure 32. Measurement of Insulation Resistance for Motor



http://www.ti.com


Insulation Resistor ( )Ω

Accura

cy

0x100 20x106 40x106 60x106 80x106 100x106-1.2%

-0.9%

-0.6%

-0.3%

0

0.3%

0.6%

0.9%

1.2%

www.ti.com Test Data

8 Test DataThe design is tested in all three configurations as explained in the following Section 8.1 throughSection 8.3.

8.1 Multiple-Shunt ApproachAs Section 5.1.2 explains, based on the insulation resistance, different shunt resistor values may berequired. To implement this change, resistors R11, R12, and R13 are switched using MOSFETs Q1 andQ2. Figure 33 shows the measurement accuracy for this approach.

Figure 33. Accuracy for Multiple Switchable Shunt Approach

As Table 5 shows, the shunt resistor value changes on-the-fly (using SW1 and SW2 signals), while theoutput of the AMC1200 must not go below 200 mV at any time.1. For an insulation resistance between 0 Ω and 3 MΩ, the value of shunt resistor is 220 kΩ || 2.7 kΩ ||

261 Ω || 28.02 kΩ.2. For an insulation resistance between 3.1 MΩ and 39.6 MΩ, the value of shunt resistor is 220 kΩ ||

2.7kΩ || 28.02 kΩ.3. For an insulation resistance between 39.7 MΩ and 98.4 MΩ, the value of shunt resistor is 220 kΩ ||

28.02 kΩ.

The accuracy graph in Figure 33 highlights the three options using different colors.

One important point to note here is the 28.02-kΩ resistance in parallel with each of the combinations,which is the input impedance of the AMC1200 device. The accuracy numbers are calibrated and accountfor the change in input impedance of the AMC1200.



http://www.ti.com


Test Data www.ti.com

Table 5. Accuracy and Measurement Table for Multiple-Shunt Approach (1)

INSULATION % ACCURACY MEASURED OUTPUT W/O VALUE OF SHUNT RESISTORRESISTOR (IN MΩ) (UNCALIBRATED) INA0.00E+00 0.41% 1.90149.98E+03 0.41% 1.86429.97E+04 0.70% 1.58446.00E+05 0.51% 0.86354 220 kΩ || 2.7 kΩ || 261 Ω || 28.02 kΩ9.89E+05 0.84% 0.638132.25E+06 0.91% 0.3463.00E+06 0.16% 0.272825.99E+06 0.12% 1.4898.97E+06 0.45% 1.022421.53E+07 0.58% 0.6148

220 kΩ || 2.7 kΩ || 28.02 kΩ2.24E+07 0.60% 0.423612.99E+07 0.47% 0.319133.96E+07 0.03% 0.24146

–0.37% 1.81694.96E+07 –10.07% 1.9842(calibrated) (calibrated)–0.80% 1.51595.93E+07 –10.24% 1.6618(calibrated) (calibrated)–0.76% 1.30066.92E+07 –9.99% 1.4254(calibrated) (calibrated)

220 kΩ || 25.75 kΩ–0.96% 1.1387.90E+07 –10.02% 1.2496(calibrated) (calibrated)–1.14% 1.012928.87E+07 –10.08% 1.1142(calibrated) (calibrated)–1.18% 0.91229.84E+07 –9.23% 1.0049(calibrated) (calibrated)

(1) The accuracy numbers are calibrated and take care of the change in input impedance of the AMC1200.



http://www.ti.com


Insulation Resistor ( )Ω

Accura

cy

0x100 20x106 40x106 60x106 80x106 100x106-4.5%

-4%

-3.5%

-3%

-2.5%

-2%

-1.5%

-1%


8.2 Single-Shunt ApproachAs Section 5.1.1 explains, the circuit can also be tested with a single shunt resistor. Figure 34 shows theaccuracy results for a single-shunt approach.

Figure 34. Accuracy for Single-Shunt Approach

As Table 6 shows, the shunt resistor value is fixed at 22 Ω. In this method, the gain of INA225 varieson-the-fly. The accuracy graph in Figure 34 shows both of the gain settings highlighted with differentcolors.

Table 6. Accuracy and Measurement Table for Single-Shunt Approach

INSULATION RESISTOR % ACCURACY VALUE OF SHUNTMEASURED O/UTPUT W/O INA(IN MΩ) (UNCALIBRATED) RESISTOR6.00E+05 –3.26% 1.93719.89E+05 –1.82% 1.45152.25E+06 –1.73% 0.78564

22 Ω (INA225 gain = 25 V/V)3.00E+06 –1.66% 0.618745.99E+06 –1.78% 0.3338.97E+06 –1.44% 0.2291.53E+07 –2.43% 1.0892.24E+07 –2.55% 0.7492.99E+07 –2.68% 0.5643.96E+07 –3.17% 0.4254.96E+07 –3.26% 0.34

22 Ω (INA225 gain = 200 V/V)5.93E+07 –3.51% 0.2846.92E+07 –3.74% 0.2437.90E+07 –3.75% 0.2138.87E+07 –4.21% 0.1899.84E+07 –4.47% 0.17



http://www.ti.com


Insulation Resistance ( )Ω

Accura

cy (

Calli

bra

ted)

0x100 5x106 10x106 15x106 20x106-0.6%

-0.4%

-0.2%

0

0.2%


8.3 Resistive Divider ApproachAs Section 5.2 explains, the circuit has an option to measure the insulation resistance using the resistivedivider approach. Figure 35 shows the accuracy results using the resistive divider approach,

Figure 35. Accuracy for Resistive Divider Approach

As Table 7 shows, the % accuracy is < 1% for a range of 0 Ω to 22.49 MΩ, but the measured output isalmost 3 mV to 4 mV different from the previous value. This difference in value means that a high-resolution ADC is required when using the resistive divider approach.

Table 7. Accuracy and Measurement Table for Resistive Divider Approach

INSULATION RESISTOR (IN MΩ) MEASURED OUTPUT VOLTAGE (IN V) % ACCURACY (CALIBRATED)10000 0.0253 -0.56%100000 0.20254 -0.09%600000 0.65263 -0.15%990000 0.79271 -0.11%2250000 0.97345 0.02%3000000 1.0186 0.01%6000000 1.09569 0.06%9000000 1.1235 0.03%14100000 1.14537 0.08%15300000 1.14847 0.09%22490000 1.1599 0.09%

To summarize the accuracy graphs, the multiple-shunt approach provides good accuracy with the entirerange covered for the insulation resistance.



http://www.ti.com



8.4 Testing Fly-Buck Power SupplyFigure 36 shows the switch node waveform at VIN = 15 V and Figure 37 shows the voltage output (3.3 V)from the non-isolated primary side of the Fly-Buck converter.

Figure 36. Switch Node Waveform at VIN = 15 V

Figure 37. 3.3-V Waveform on Primary Side of LM5160 Fly-Buck Design



http://www.ti.com



Figure 38 shows the voltage output (6V_VCC1) from the isolated secondary side of the Fly-Buckconverter. Figure 39 shows the 5V_VCC1 derived from 6V_VCC1 using the TLV1117-50 device.

Figure 38. 6V_VCC1 Waveform




http://www.ti.com



Figure 40 shows the voltage output (6V_VCC2) from the isolated secondary side of the Fly-Buckconverter. Figure 41 shows the 5V_VCC2 derived from 6V_VCC2 using the LP2985A-5.0 device.





http://www.ti.com



Now view the ripple voltage on each of the outputs. Figure 42 shows the ripple measured on a 3.3-Voutput on the primary side of the Fly-Buck converter.

Figure 42. Ripple Measured on 3.3-V Output



http://www.ti.com



Figure 43 and Figure 44 show the ripple on 6V_VCC1 and 5V_VCC1 respectively.

Figure 43. Ripple Measured on 6V_VCC1 Output




http://www.ti.com



Figure 45 and Figure 46 show the ripple on 6V_VCC2 and 5V_VCC2 respectively.

Figure 45. Ripple on 6V_VCC2 Output




http://www.ti.com


Input Voltage (V)

Regula

tion

100 200 300 400 500 600 700 8000.35%

0.4%

0.45%

0.5%

0.55%

0.6%

0.65%

0.7%

0.75%

0.8%

0.85%

0.9%

0.95%

1%

1.05%

1.1%

1.15%

Input Voltage (V)

Regula

tion

100 200 300 400 500 600 700 800-0.6%

-0.5%

-0.4%

-0.3%

-0.2%

-0.1%

0

0.1%

0.2%

0.3%

0.4%


8.5 Testing TIDA-00440DB Flyback Power SupplyThe flyback design was tested for line regulation at no-load condition and at a load of 1.5 mA. Figure 47shows the regulation during no-load condition:

Figure 47. Line Regulation at No Load

Figure 48 shows the regulation with a load of 1.5 mA:

Figure 48. Line Regulation at Load = 1.5 mA



http://www.ti.com



Figure 49 shows the output ripple at the no-load condition.

Figure 49. Output Ripple Waveform at No-Load

Figure 50 shows the output ripple at a load current of 1.5 mA.

Figure 50. Output Ripple Waveform at Load = 1.5 mA



http://www.ti.com



8.6 Testing With 2HP 3-Ph AC Induction MotorAs Figure 51 shows, the TIDA-00440 reference design was tested with a motor. The insulation resistancemeasurement takes place between one of the motor terminals (yellow wire in this example ), and theframe of the motor (black wire). Figure 52 shows a zoomed-in version of the motor section. The motorused for this experiment is a 2-hp, three-phase AC induction motor. The insulation resistance of this motor(measured with high-resistance measurement equipment from Keithley) is 547 MΩ.

For the sake of measurement, one 100-MΩ resistance is connected in parallel with the motor insulation.The parallel combination is measured with the TIDA-00440 device. After doing this check, the insulationresistance is 547 MΩ || 100 MΩ = 84.54 MΩ (theoretically). Table 8 shows the actual values of insulationresistance measured with the single-shunt approach and the multiple-shunt approach.

Table 8. Insulation Resistance Measured With Motor

VOLTAGE OUTPUT CORRESPONDING INSULATIONTEST CONDITION MEASURED RESISTANCESingle-shunt approach (INA225 gain = 200, RSHUNT = 22 Ω) 0.20953 V 83.497 MΩMultiple-shunt approach (RSHUNT = 220 kΩ || 2.7 kΩ || 261 Ω),MUX = 1, removed 10-Ω resistors from the front filter of 1.154 V 85.65 MΩINA225)

Figure 51. Motor Used for Testing TIDA-00440 Figure 52. Zoomed-In Photo of of Motor Used for TestingTIDA-00440



http://www.ti.com


Design Files www.ti.com

9 Design Files

9.1 SchematicsTo download the schematics for each board, see the design files at http://www.ti.com/tool/TIDA-00440.

9.2 Bill of MaterialsTo download the bill of materials (BOM), see the design files at http://www.ti.com/tool/TIDA-00440.

9.3 PCB Layout RecommendationsAn important thing to note is that the design contains high voltages up to 500 V and 800 V. The layoutmust be done with extreme care.

9.3.1 Layout Recommendations for TIDA-00440MBThe total size of the main board is 124.46 mm x 110 mm. Banana jacks J1 and J2 are used for an inputvoltage of 150-V DC to 800-V DC. J3 and J4 are used to connect the insulation resistance. Figure 53shows how the clearances are provided on the PCB for the isolations.

Figure 53. Clearance for Isolation

9.3.2 Layout Recommendations for LM5160 Fly-Buck Power SupplyA proper layout is essential for optimum performance of the circuit. Figure 54 shows the layout of theLM5160 Fly-Buck section.

Figure 54. Layout for Fly-Buck Power Supply Section



http://www.ti.com




www.ti.com Design Files

In particular, the following guidelines must be observed:• The loop consisting of the input capacitor, VIN pin, and PGND pin carries the switching current.

Therefore, the input capacitor must be placed close to the IC, directly across the VIN and PGND pins.The connections to these two pins must be direct to minimize the loop area. In general, placing all ofthe input capacitances near the IC is not a possibilty. A good practice is to use a 0.1- to 0.47-μFcapacitor directly across the VIN and PGND pins as close as possible to the IC with the remaining bulkcapacitor.

• The VCC and bootstrap (BST) bypass capacitors supply switching currents to the high and low-sidegate drivers. These two capacitors must also be placed as close to the IC as possible, and theconnecting trace length and loop area must be minimized.

• The feedback trace carries the output voltage information and a small ripple component that isnecessary for proper operation of the LM5160 device. Therefore, take care while routing the feedbacktrace to avoid coupling any noise into the feedback (FB) pin. In particular, the feedback trace must notrun close to magnetic components, or parallel to any other switching trace.

• SW trace: The SW node switches rapidly between VIN and GND every cycle and is therefore a sourceof noise. The SW node area must be minimized. In particular, the SW node must not be inadvertentlyconnected to a copper plane or pour.

Figure 55 shows a zoomed-in image of components near the LM5160 device.

Figure 55. Component Placements Near LM5160



http://www.ti.com



9.3.3 Layout Recommendations for TIDA-00440DBA good layout is critical for proper functioning of the power supply. Figure 56 shows the overall layout ofthe daughter board. The total size of the daughter board is 75 mm x 52 mm.

Some critical points to note for the UCC28711 device are:1. The loop of the current sense resistor, power MOSFET, transformer, and input bulk cap must be as

small as possible (see Figure 57).2. There must be a single point ground for the controller IC.3. The control ground and power ground must be connected at a single point, which is the input bulk

capacitor (see Figure 58 and Figure 59).

Figure 56. Layout for TIDA-00440DB

Figure 57. Power Loop Shown With White Line



http://www.ti.com


www.ti.com Design Files

Figure 58. Single-Point Ground (Bottom Layer)

Figure 59. Single-Point Ground (Top Layer)



http://www.ti.com



9.4 Layout PrintsTo download the layout prints for each board, see the design files at http://www.ti.com/tool/TIDA-00440.

9.5 Altium ProjectTo download the Altium project files, see the design files at http://www.ti.com/tool/TIDA-00440.

9.6 Gerber FilesTo download the Gerber files, see the design files at http://www.ti.com/tool/TIDA-00440.

9.7 Assembly DrawingsTo download the assembly drawings, see the design files at http://www.ti.com/tool/TIDA-00440.

9.8 Software FilesTo download the software files, see the design files at http://www.ti.com/tool/TIDA-00440.

10 References

1. IEEE.org, IEEE Standards Association, 43-2000 - IEEE Recommended Practice for Testing InsulationResistance of Rotating Machinery

2. Chafai, Mahfoud; Refoufi, Larbi; Bentarzi, Hamid; Signals and Systems Laboratory (SisyLab),Medium Induction Motor Winding Insulation Protection System Reliability Evaluation and Im provementUsing Predictive Analysis , DGEE, FSI, University of Boumerdes, Algeria

11 About the AuthorSANJAY PITHADIA is a Systems Engineer at Texas Instruments where he is responsible for developingsubsystem design solutions for the Industrial Motor Drive segment. Sanjay has been with TI since 2008and has been involved in designing products related to Energy and Smart Grid. Sanjay brings to this rolehis experience in analog design, mixed signal design, industrial interfaces and power supplies. Sanjayearned his Bachelor of Technology in Electronics Engineering at VJTI, Mumbai.

PAWAN NAYAK is a Systems Engineer at Texas Instruments where he is responsible for developingreference design solutions for the Motor Drive segment within Industrial Systems. Pawan brings to thisrole his experience in analog system design, mixed signal design and power supplies. Pawan earned hisBachelor of Engineering in Electronics and Communication Engineering from Visvesvaraya TechnologicalUniversity, India.

N. NAVANEETH KUMAR is a Systems Architect at Texas Instruments, where he is responsible fordeveloping subsystem solutions for motor controls within Industrial Systems. N. Navaneeth brings to thisrole his extensive experience in power electronics, EMC, Analog, and mixed signal designs. He hassystem-level product design experience in drives, solar inverters, UPS, and protection relays. N.Navaneeth earned his Bachelor of Electronics and Communication Engineering from BharathiarUniversity, India and his Master of Science in Electronic Product Development from Bolton University, UK.



http://www.ti.com







m PRI SECi i Ni= +

VINVSEC

VPRI

N

1

VDA

iOSEC

iOPRI

GND

iGND

VSW

iPRI

VINVSEC

VPRI

N

1

VDA

iOSEC

iOPRI

GND

iGND

VSW

iPRI

ISEC

a) During TON b) During TOFF

VIN

VOUT

VINVSEC

VPRI

N

1

+

-

BuckFly-Buck

+ =

Appendix A—Fly-Buck Power SupplyThe Fly-Buck is basically a buck regulator with couple windings added to the inductor. The coupledwindings can generate isolated outputs. The physical appearance of the Fly-Buck resembles acombination of a buck and flyback converter, hence the name Fly-Buck (Figure 60). The operation on theprimary side is similar to the buck, while the secondary side output is clamped by the primary output. TheFly-Buck operation in a switching cycle can be divided into on-time and off-time, as Figure 61 shows.

Figure 60. From Buck to Fly-Buck

Figure 61. The Fly-Buck in ON and OFF time

During TON, the rectifier diode is in reverse bias, so the secondary side is cut off from the primary. Theprimary side operates similarly as it does in a buck regulator; the transformer primary current rises linearly.The primary output voltage is Vpri = D × VIN. During TOFF, the diode is forward biased and conducts. Thecurrent can flow in the primary and secondary side simultaneously; however, the magnetizing current inthe transformer is still in the triangle waveform, which can be calculated as the combination of the primaryand secondary winding current as defined by Equation 2:

(2)




m_PEAK m m opri osec m

1 1i i i i (N i ) i

2 2= + D = + ´ + D

PRIm

PRI SW

V 1 Di

L f

-D =

VSW

VIN

GND

VSEC

TON TOFF

iGND

-n(VIN-VPRI)

im=iPRI+NiSEC

VDA

iOPRI+niOSEC

iPRI

iSEC

iOPRI

iOSEC

0At

t

t

t

t

www.ti.com

The primary side output clamps the secondary output voltage, VSEC = N × VPRI. View the steady-stateoperation waveforms of a Fly-Buck in Figure 62.

Figure 62. Fly-Buck Operation Waveform

From the preceding analysis, the magnetizing current ripple can be derived as Equation 3:

where• LPRI = Primary inductance• D = TON / (TON + TOFF) = Duty cycle• fSW = Switching frequency (3)

Equation 4 calculates the peak current of the primary side as:

where• iopri = Average primary output current• iosec = Average secondary output current (4)

If multiple outputs are involved, each secondary output must be converted to the primary side bymultiplying the corresponding turns-ratio — Equation 2 is still applicable.



http://www.ti.com


CCR PSCS XFMR

OCC

V NR

2I

´= ´ h

S1 VSRS2

AS OCV F VSR

R VR

N (V V ) V

´

=

´ + -

IN_RUNS1

PA VSL _RUN

VR

N I=

´

www.ti.com

Appendix B—PSR Flyback Power SupplyThe UCC28711 is a PSR flyback controller. In primary-side control, the output voltage is sensed on theauxiliary winding during the transfer of transformer energy to the secondary. To achieve an accuraterepresentation of the secondary output voltage on the auxiliary winding, the discriminator (insideUCC28711) reliably blocks the leakage inductance reset and ringing, continuously samples the auxiliaryvoltage during the down slope after the ringing is diminished, and captures the error signal at the time thesecondary winding reaches zero current. The internal reference on VS is 4.05 V; and VS is connected to aresistor divider from the auxiliary winding to the ground. The output-voltage feedback information issampled at the end of the transformer secondary-current demagnetization time to provide an accuraterepresentation of the output voltage. Timing information to achieve valley switching and to control the dutycycle of the secondary transformer current is determined by the waveform on the VS pin. TI does notrecommend to place a filter capacitor on this input, which would interfere with accurate sensing of thiswaveform. The VS pin senses the bulk-capacitor voltage to provide for AC-input run and stop thresholds.The VS pin also compensates the current-sense threshold across the AC-input range. The VS pininformation is sensed during the MOSFET on-time. For the AC-input run or stop function, the run thresholdon VS is 225 μA and the stop threshold is 80 μA. A wide separation of run and stop thresholds allowsclean startup and shutdown of the power supply with the line voltage. The values for the auxiliary voltagedivider upper-resistor RS1 and lower-resistor RS2 can be determined by Equation 5 and Equation 6.

where• NPA is the transformer primary-to-auxiliary turns ratio• VIN_RUN is the converter input start-up (run) voltage• IVSL_RUN is the run threshold for the current pulled out of the VS pin during the MOSFET on-time (equal to 220

μA max from the UCC28711 data sheet) (5)

where• VOCV is the regulated output voltage of the converter• VF is the secondary rectifier forward voltage drop at near-zero current• NAS is the transformer auxiliary-to-secondary turns ratio• RS1 is the VS divider high-side resistance• VVSR is the CV regulating level at the VS input (equal to 4.05 V typical from the UCC28711 data sheet) (6)

The UCC28711 device operates with cycle-by-cycle primary-peak current control. The normal operatingrange of the CS pin is 0.78 V to 0.195 V. There is additional protection if the CS pin reaches 1.5 V, whichresults in a UVLO reset and restart sequence. The current-sense (CS) pin is connected through a seriesresistor (RLC) to the current-sense resistor (RCS). The current-sense threshold is 0.75 V for IPP_MAX and0.25 V for IPP_MIN. The series resistor RLC provides the function of feed-forward line compensation toeliminate any change in IPP due to change in di/dt and the propagation delay of the internal comparatorand MOSFET turnoff time. There is an internal leading-edge blanking time of 235 ns to eliminatesensitivity to the MOSFET turn-on current spike. The value of RCS is determined by the target outputcurrent in constant-current (CC) regulation, as Equation 7 shows. The value of RLC is determined byEquation 8.

where• RCS is the current sense resistor value• VCCR is the current regulation constant (equal to 330 mV typical from the UCC28711 data sheet)• NPS is the transformer primary-to-secondary turns ratio• IOCC is the target output current in constant-current regulation• ηXFMR is the transformer efficiency (7)



http://www.ti.com


LC S1 CS D PALC

P

K R R T NR

L

´ ´ ´ ´

=

www.ti.com

where• RLC is the line compensation resistor• RS1 is the VS pin high-side resistor value• RCS is the current-sense resistor value• TD is the current-sense delay including MOSFET turn-off delay (add 50 ns to the MOSFET delay)• NPA is the transformer primary-to-auxiliary turns ratio• LP is the transformer primary inductance• KLC is the current-scaling constant (equal to 25 A/A according to the data sheet of UCC28711) (8)



http://www.ti.com


IMPORTANT NOTICE FOR TI REFERENCE DESIGNS

Texas Instruments Incorporated ("TI") reference designs are solely intended to assist designers (“Buyers”) who are developing systems thatincorporate TI semiconductor products (also referred to herein as “components”). Buyer understands and agrees that Buyer remainsresponsible for using its independent analysis, evaluation and judgment in designing Buyer’s systems and products.TI reference designs have been created using standard laboratory conditions and engineering practices. TI has not conducted anytesting other than that specifically described in the published documentation for a particular reference design. TI may makecorrections, enhancements, improvements and other changes to its reference designs.Buyers are authorized to use TI reference designs with the TI component(s) identified in each particular reference design and to modify thereference design in the development of their end products. HOWEVER, NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPELOR OTHERWISE TO ANY OTHER TI INTELLECTUAL PROPERTY RIGHT, AND NO LICENSE TO ANY THIRD PARTY TECHNOLOGYOR INTELLECTUAL PROPERTY RIGHT, IS GRANTED HEREIN, including but not limited to any patent right, copyright, mask work right,or other intellectual property right relating to any combination, machine, or process in which TI components or services are used.Information published by TI regarding third-party products or services does not constitute a license to use such products or services, or awarranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectualproperty of the third party, or a license from TI under the patents or other intellectual property of TI.TI REFERENCE DESIGNS ARE PROVIDED "AS IS". TI MAKES NO WARRANTIES OR REPRESENTATIONS WITH REGARD TO THEREFERENCE DESIGNS OR USE OF THE REFERENCE DESIGNS, EXPRESS, IMPLIED OR STATUTORY, INCLUDING ACCURACY ORCOMPLETENESS. TI DISCLAIMS ANY WARRANTY OF TITLE AND ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESSFOR A PARTICULAR PURPOSE, QUIET ENJOYMENT, QUIET POSSESSION, AND NON-INFRINGEMENT OF ANY THIRD PARTYINTELLECTUAL PROPERTY RIGHTS WITH REGARD TO TI REFERENCE DESIGNS OR USE THEREOF. TI SHALL NOT BE LIABLEFOR AND SHALL NOT DEFEND OR INDEMNIFY BUYERS AGAINST ANY THIRD PARTY INFRINGEMENT CLAIM THAT RELATES TOOR IS BASED ON A COMBINATION OF COMPONENTS PROVIDED IN A TI REFERENCE DESIGN. IN NO EVENT SHALL TI BELIABLE FOR ANY ACTUAL, SPECIAL, INCIDENTAL, CONSEQUENTIAL OR INDIRECT DAMAGES, HOWEVER CAUSED, ON ANYTHEORY OF LIABILITY AND WHETHER OR NOT TI HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, ARISING INANY WAY OUT OF TI REFERENCE DESIGNS OR BUYER’S USE OF TI REFERENCE DESIGNS.TI reserves the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services perJESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevantinformation before placing orders and should verify that such information is current and complete. All semiconductor products are soldsubject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s termsand conditions of sale of semiconductor products. Testing and other quality control techniques for TI components are used to the extent TIdeems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is notnecessarily performed.TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products andapplications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provideadequate design and operating safeguards.Reproduction of significant portions of TI information in TI data books, data sheets or reference designs is permissible only if reproduction iswithout alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable forsuch altered documentation. Information of third parties may be subject to additional restrictions.Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirementsconcerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or supportthat may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards thatanticipate dangerous failures, monitor failures and their consequences, lessen the likelihood of dangerous failures and take appropriateremedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components inBuyer’s safety-critical applications.In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is tohelp enable customers to design and create their own end-product solutions that meet applicable functional safety standards andrequirements. Nonetheless, such components are subject to these terms.No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the partieshave executed an agreement specifically governing such use.Only those TI components that TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use inmilitary/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components thathave not been so designated is solely at Buyer's risk, and Buyer is solely responsible for compliance with all legal and regulatoryrequirements in connection with such use.TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use ofnon-designated products, TI will not be responsible for any failure to meet ISO/TS16949.IMPORTANT NOTICE

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265Copyright © 2015, Texas Instruments Incorporated

tidu873a | ti.com - semiconductor company | ti.com

Documents